Production of sulphur



May 1.4, 1940- H. BAEHR l-:T AL

FRODUCTION OF SULPHUR Filed June 10.*193'7 sri/w H, 5 sap Hans .Bae/zr,Karl -B?us INVENTORS TH EIR ATTORNEYS Patented May 14, 1940 UNITEDSTATES PATENT OFFICE PRODUCTION F SULPH'UR Application June 10, 1937,Serial No. 147,412

In Germany June 13, 1936 4 Claims.

The present invention relates to the production of sulphur from hydrogensulphide or gases rich in hydrogen sulphide.

Attempts have already been made to obtain sulphur from hydrogen sulphideor gases rich in hydrogen sulphide by combustion with a free i'lame withthe aid of as much oxygen or gases containing oxygen as is necessary forthe conversion of the hydrogen sulphide into sulphur. Such attempts havehitherto been unsuccessful, however, because the combustion of hydrogensulphide does not proceed uniformly, so that at times sulphur isobtained While at other times no conversion of the hydrogen sulphide'takes place. Combustion with a free ame has therefore been abandonedfor the purpose of producing sulphur from hydrogen sulphide and theconversion has been carried out according to the proposals of Claus by acatalytic method instead. This method of working has the great drawback,however, that the permissible loading of the catalyst, i. e. the amountof gas which can be treated by a given amount of catalyst per unit oftime, is extremely small as compared with other catalytic reactions. Byreason of the necessity for maintaining relatively low temperatures,only about 4 cubic meters of hydrogen sulphide can be converted per hourper cubic meter of catalyst. The process therefore requires extremelybulky apparatus which not only occasion high erection costs but whichalso require a large amount of space.

We have now found that. the conversion of hydrogen sulphide or gasescontaining hydrogen sulphide into sulphur by combustion in a free llamewith an amount of oxygen or gases containing elementary oxygen which issmaller than that required for the conversion of the hydrogen sulphideinto sulphur dioxide can be'carried out in a simple manner bymaintaining at a place of the ame zone, i. e. within the flame or at aplace in its direct neighbourhood, so high a temperature that the llameis continuously maintained and any extinguishing of the flame isavoided. This may be effected in a simple manner for example byarranging suitable heating bodies in the ame zone, the said heatingbodies being heated to the necessary temperature for example byelectricalmeans. It is, however, even more simple to carry out thecombustion in a closed chamber the Walls of which have been brought tothe necessary temperature before the beginning of the conversion. Thesaid Walls may be externally protected against heat lossesby suitableinsulation. It is even more simple to (Cl. 2li- 226) line the walls ofthe combustion chamber with refractory bricks which, once they have beenbrought to the necessary temperature, are kept at the said temperatureby the heat formed during the reaction. As a rule, the technicallyavail- 5 able apparatus for burning combustible gases, as for examplethe fire-boxes of boilers, may be used for the process without furtheralteration. Such apparatus usually accumulate sumcient heat to maintainthe aforesaid conditions.

The minimum temperature necessary depends on the one hand on thehydrogen sulphidev content of the gases, which should as a rule be atleast per cent and preferably at least 15 per cent, and on the otherhand on the amount of 15 oxygen present during the combustion. Thetemperature may be lower the higher the concentration of the hydrogensulphide in the gas containing hydrogen sulphide to be burned on the onehand and the larger the amount of oxygen or gas containing elementaryoxygien supplied -for the conversion on the other hand. For example whenWorking with practically pure hydrogen sulphide and. eifecting thecombustion with such an amount of air that the amount of free oxygen isjust sumcient for the conversion of the hydrogen sulphide into sulphur,it is usually suflicient for the heated or heat-accumulating placewithin the flame or in its neighbourhood to have a temperature of about250 C. If 30 it is desired tov burn gases lower in hydrogen sulphide, asfor example those containing 20 per cent of hydrogen sulphide, atemperature of at least about 700 C. must be maintained in the heated orheat-accumulating place. As a rule it is sufcient to use temperatures ofabout dark red heat, for example from about 500 to 600 C. When workingwith the said gases in a combustion chamber which is lined withrefractory bricks, a temperature of from about 800 to 1000 C. is usuallyset up in the same.

The hydrogen sulphide may also be introduced into the combustion chamberin two or more stages so that at first a part of the hydrogen sulphidereacts with the Whole amount of oxygen necessary for the conversion,whereby a high temperature may readily be maintained. Following on thiscombustion, the remainder of the hydrogen sulphide may be supplied.

When employing for the conversion just the amount of oxygen necessaryfor the conversion of the whole of the hydrogen sulphide into sulphur,there are present in the combustion gases after cooling from about 80 to90 per cent of the hydrogen sulphide used in the form of sulphur.

'I'his result is the more surprising because the combustion temperaturefor example in the case of per cent hydrogen sulphide and the amount ofair equivalent for conversion into sulphur is about 1000 C. and theequilibrium between hydrogen sulphide, sulphur dioxide and sulphur isknown to be favourable for the formation of sulphur at low temperaturesonly, so that for example in the catalytic conversion without a freeflame in a Claus furnace with a catalyst temperature of 500 C. onlyabout 50 per cent of the hydrogen sulphide, and at higher temperatm'eseven less thereof, is converted into sulphur.

'I'he combustion of the'hydrogen sulphide according to this invention ispreferably effected beneath a steam boiler, whereby the heat developedduring the combustion is utilized for the production of steam in theboiler and for the superheating of the steam and if necessary also forthe preheating of the water supplied to the boiler.

Since sulphur solidies at 114 or 119 C., an operating pressure for thesteam boiler is used such that the boiling temperature of the water liesabove 119 C., i. e. a pressure of Vat least 2 atmospheres. When usingfire-tube boilers, the cooling of the combustion gases can be mostsimply effected without the aid of the preheater for the supply water,i. e. merely in the firetubes. It is also advantageous to have regard tothe property of sulphur of being very nobile up to 150 C. Therefore,when there are no other reasons for selecting higher or lower operatingpressures of the boiler, there is selected for example a fire-tubeboiler for the production of steam at about 4 atmospheres, whereby thesulphur by condensation on the re-tubes separates in a Very mobile formand therefore runs away especially readily.

When using preheaters for the supply water for the cooling of thecombustion gases, care must be taken that the supply water enters thepreheater at a. temperature of at least 119 C. because otherwise thesulphur would solidify on the preheater tubes. For example the supplywater may be rst heated in a. preheater ar ranged outside the boilerwith a small part of the steam produced in the boiler, for example to120 C., the supply water thus heated then being led, together with thecondensed steam, into the preheater heated by the combustion gases. Itis advantageous to arrange the single parts of the boiler so that thesulphur separated in the liquid state by the cooling of the combustiongases can ow away from the boiler parts in the direction of the streamof gas.

The fire-box of the boiler is internally lined with several layers oflire-brick so that the iron outer shell of the lire-box does not attaintemperatures substantially above 100 C. Contrary to expectation, nosulphurization or corrosion of the metal parts of the boiler takes placein spite of the high concentration of the vaporous sulphur in thecombustion gases and in spite of the separation of the liquid sulphur onthe metal parts of the boiler, provided temperatures of between 330 to350 C, are not exceeded. If that condition cannot be maintained, it ispreferable to protect the metallic parts by a zinc coating which may beapplied by dipping the material in a hot bath of liquid zinc or also byexposing the metallic parts to an atmosphere of zinc vapor at hightemperatures. It should be noted, however, that the metallic parts ofthe boiler should not have a temperature far below 100 C. becauseotherwise the dew point of thc combustion gases may be reached and acidcondensates having a. corrosive action may be formed.

In order to separate the sulphur still present in the combustion gasesafter leaving the boiler, the gases must be cooled to at least about200" C., advantageously to a still lower temperature. If possible, thegases are cooled to a temperature in the neighborhood of 120 C., sinceonly at such comparatively low temperatures the vapor tension of sulphuris suiliciently low to render possible a complete separation of thesulphur.

The cooled gases may be led in known manner for example throughelectro-filters or so-called multiclones" (which consist of a pluralityof cyclones arranged in parallel and enclosed in a common housing) orthrough separators filled with Raschig rings or through similar devicesin which the sulphur separates.

Instead of cooling the combustion gases in a steam boiler, they may becooled for example with air or oil coolers or the gases may be cooled byspraying in water, in which case it is preferable to use water underpressure which is heated to above 100 C.

If the amount of hydrogen sulphide to be converted into sulphur varies,provision is made for the continuous maintenance of the requisite amountof oxygen or gases containing oxygen by means of control apparatus ofknown con- I struction. When gases containing varying amounts ofhydrogen sulphide are treated,'it is preferable to use automaticanalysis apparatus which at the same time control the amount of oxygenor gases containing oxygen supplied to the combustion chamber.

When it is suflicient to convert from about to per cent of the hydrogensulphide into sulphur, the combustion gases, after the separation of thesulphur, may if desired be led through sulphur dust chambers and theninto a chimney or for example into an ordinary boiler ring.

If,'on the other hand, it is desired to convert the hydrogen sulphide ascompletely as possible into sulphur, the combustion gases, after coolingand if desired after separation of sulphur, are led in known manner overcatalysts for the conversion of the hydrogen sulphide still present. Inthis case, in contrast to the usual Claus process, the catalyst may beloaded about times more strongly by reason of the only slight heat ofreaction, which usually occasions a rise in temperature of only about 50C. Before entry to the catalyst the combustion gases are cooled nofurther than to the lower reaction limit of the catalyst. It is alsopreferable, when the combustion gases are strongly cooled before entryto the catalyst, to provide for as complete a separation of the sulphuralready formed as possible, because it would otherwise be precipitatedin the first layers of catalyst and might give rise to stoppagestherein.

If such a far-reaching separation of the sulphur already formed isdispensed with, the working temperature in the layer of catalyst must becorrespondingly higher; for example the gases may be introduced into thecatalyst at a temperature of 220 C. It a boiler is used, the catalystmay be arranged at any place outside or inside the boiler. For exampleit maybe arranged in the boiler outlet or even in the fire-tubes of theboiler. Frequently it is preferable to subdivide the catalyst into twolayers and toprovide a gas cooling and simple separation of sulphurbetween the two layers. Since the reaction when inuenced by catalystsproceeds more completely the lower the reaction temperature is, thesubdivision of the catalyst layer with an intermediate cooling andseparation of sulphur facilitates the complete conversion of thehydrogen sulphide into sulphur.

In case it is desired to convert part of the hydrogen sulphide intosulphur and the remainder into sulphur dioxide, the combustion may becarried through with so much oxygen or gases containing oxygen that thepercentage of the hydrogen sulphide which is not to be converted intosulphur is directly burnt to sulphur dioxidef For example, if one thirdof the hydrogen sulphide is to be converted into sulphur and the othertwo thirds into sulphur dioxide, the hydrogen sulphide is burnt with 5.6times its amount of air. Combustion gases are then obtained in a singleoperation which contain one third-of the hydrogen sulphide in the formof sulphur and two thirds in the form of'sulphur dioxide. Whenthesulphur has been separated from these gases, sulphur dioxide is left.This method has the advantage that the sulphur dioxide is free fromsulphur trioxide so that the risk of corrosion is reduced.

The process according to this invention is capable of being adapted to agreat extent to the requirements in any single case. For example if itis desired to obtain from the hydrogen sulphide, not only sulphur butalso sulphuric acid.

the hydrogen sulphide is burned with an amount of air or omgen such asis necessary for the formation of the desired amount of sulphur. Thecombustion gases are then cooled and the sulphur formed separated. Theresidual gas is then burned with an excess of oxygen oroxygen-containing gas, if desired with the aid of catalysts, to formsulphur dioxide which may then be converted into sulphuric acid in knownmanner.

If, in addition to hydrogen sulphide, there is also available sulphurdioxide or gases containing the same, the latter may also be rendereduseful for the production of sulphur by supplying sulphur dioxide to thegases containing hydrogen sulphide before or during the combustion in afree ame. The amount of oxygen or oxygencontaining gas may then becorrespondingly smaller but must, however, always be suiilciently greatthat the combustion with the free flame proceeds without trouble. In thesame way sulphur trioxide or even sulphuric acid may be supplied insteadof sulphur dioxide and also converted into sulphur.

The following examples will further illustrate the nature of thisinvention, of which Example 1 is given with reference to theaccompanying drawing which shows diagrammatically a vertical section ofan arrangement of apparatus suitable for carrying out the processaccording to this invention; but the invention is restricted neither to.

these examples nor to the particular arrangement shown.

Ensamble 1- 1500 cubic meters of a gas containing per cent of hydrogensulphide and 40 per cent of carbon dioxide are burned per hour with 2160 cubic meters of air in the combustion chamber I o f a verticalnre-box boiler 2 for the production of steam at a pressure of 16atmospheres. The gas containing hydrogen sulphide is supplied through apipe 3 and the air through a pipe 4. The combustion chamber of theboiler is lined with refractory bricks 5 and is brought, before thebeginning of the reaction, to the necessary temperature, i. e. at leastto dark red heat, either by burning la heating gas or by burning the gascontaining hydrogen sulphide with an excess of air. Within the boiler inthe path of the combustion gases above the boiler tubes 6 (shown inbroken lines) there are arranged a steam superheater 1 and a supplywater preheater 8 through which the combustion gases pass downwards.Into the preheater 8 there is led supply water which has previously beenheated to at least 120 C. in a special preheater 9, arranged outside theboiler, mth the aid of steam supplied through a pipe The combustiongases, which contain an amount of Vaporous sulphur corresponding toabout per cent of the hydrogen sulphide introduced into the vcombustionchamber and also 3 per cent of hydrogen sulphide and 1.5 per cent ofsulphur dioxide, are led to the supply water preheater 8 after passagethrough the steam superheater 1. The amount of water supplied to thesupply water preheater 8 and its temperature are so regulated that thecombustion gases are cooled Ato 180 C. therein. In this way half of thesulphur contained in the gases is separated in liquid form. The gasesare then led at the same temperature through a so-called multiclone Ilfor the recovery of the remaining sulphur. There are obtained per hour1020 kilograms of liquid sulphur in all and also 2.1 metric tons ofsuperheated steam under a pressure of 16 atmospheres. The combustiongases are then led through so-called dust chambers (not shown) in whichthe `greater part of the hydrogen sulphide and sulphur dioxide stillcontained therein are w converted rinto sulphur and are then led to achimney. I

- .Eample 2 For converting practically pure hydrogen sulphide in anamount of 500 cubic meters per hour practically completely into sulphurthe gas is burnt with 1200 cubic meters of air perhour in I the fire-boxof a horizontal fire-tube boiler which is downwardly inclined'in thedirection of the flow of the gases. internally lined with so many layersof nre-brick that the iron shell of the nre-box does not becomesubstantially hotter than C. In the boiler, steam of 4 atmospherespressure is produced.

,The boiler is provided not only with the usual comparatively narrownre-tubes, but also with'a comparatively wide tube which may be closedor opened at will by means of a conical stopper at the gas exit side.When the stopper is closed, the gases must pass exclusively through thenarrow fire-tubes and are then cooled comparatively strongly by thewater surrounding the lre tubes. If, however, the stopper in the widetube is opened', a large amount of gas will pass through catalyst, thetemperature of the gasesis increased. by about 100 C., i. e. to about350 C. The gases then pass through a separating chamber of about 6 cubicmeter capacity arranged below the catalyst in which the gases are cooledto about The fire-box of the boiler is CII 180 C. The gases are thenheated to about 250 C. by the combustion heat supplied by burning asmall amount of hydrogen sulphide with 2.4 times its amount of air andare then introduced into a y second bauxite catalyst of about 3 cubicmeters similar to the first one. The gases leaving this second catalystpass through an electrostatic lter which they leave with a temperatureof about 130 C.

During the combustion in the boiler, about 80 per cent of the hydrogensulphide is converted into sulphur. v'I'he gases contain, in addition tonitrogen and water vapor, hydrogen sulphide and sulphur dioxide in theproportion of 2:1. These latter constituents are converted in the rstcatalyst layer so far that the total yield in sulphur amounts to 90 percent and in the second catalyst layer so far that-the total yield is 95per cent. Of the sulphur formed, about one ilfth is separated intheliquid state in the boiler, about three fths below the two catalysts,and the last tlfth in the electro-filter. 'I'he liquid sulphur may bewithdrawn from each place into'a common collecting vessel.

IfI the combustion of the hydrogen sulphide in the boiler would beomitted, the cataylsts would be able to convert only about 12 cubicmeters of hydrogen sulphide per hour into sulphur and the yield wouldonly be 85 per cent.

What we claim is:

1. The process of producing sulphur which comprises burning a gascomprising a substantial amount of hydrogen sulphide in a free llamewith an amount of a gas comprising elementary oxygenwhich is smallerthan that required for the conversion of all of the hydrogen sulphideinto sulphur dioxide but is suilicient to convert the hydrogen sulphideto free sulphur, maintaining at a place of the flame zone so high atemperature that the flame is continuously maintained, cooling the`resulting gas, separating sulphur therefrom and passing the remaininggas over a catalyst for converting the remainder of the hydrogensulphide into sulphur in accordance with the Claus process,

2. 'I'he process of producing sulphur which comprises burning a gascomprising a substantial amount of hydrogen sulphide in a tree flamewith an amount of a gas comprising elementary oxygen which is smallerthan that required for the conversion of all of the hydrogen sulphideinto sulphur dioxide but is sufllcient to convert the hydrogen sulphideto free sulphur, maintaining at a place of the name zone so high atemperature that the llame is continuously maintained, cooling theresulting gas and passing it over a catalyst for converting theremainder of the hydrogen sulphide into sulphur in accordance with theClaus process.

3. The process oi' .producing sulphur which comprises burning in thepresence of sulphur dioxide a gas comprising a substantial amount ofhydrogen sulphide in a tree llame with an amount of a gas comprisingelementary oxygen which is smaller than that required for the conversionof all of the hydrogen sulphide into sulphur dioxide but is sumcient toconvert the hydrogen sulphide to free sulphur, maintaining at a place ofthe ame zone so high a temperature that the flame is continuouslymaintained, cooling the resulting gas and passing it over a catalyst forconverting the remainder of the hydrogen sulphide into sulphur inaccordance with the Claus process.

4. The process of producing sulphur which comprises burning a gascomprising a substantial amount of hydrogen sulphide in a free ame withan amount of a gas comprising elementary oxygen which is smaller thanthat required for the conversion of all of the hydrogen sulphide intosulphur dioxide but is sufllcient to convert the hydrogen sulphide tofree sulphur. maintaining at a place of the flame zone so high atemperature that the flame is continuously maintained, transferring heatfrom the resulting combustion gases to a body of water, therebyproducing steam and simultaneously cooling the combustion gas, andpassing said combustion gas over a catalyst for converting the remainderof the hydrogen sulphide into sulphur in accordance with the Clauspl'OCeSS.

HANS BAEHR.

KARL BRAUS.

